Hydrocarbon conversion



Patented Dec. 14, 1943 HYDROCARBON CONVERSION Q Hugh S. Taylor and Harold Fehrer, Princeton,

N. J., assignors to Process Management Company, Inc., Wilmington, DeL, a corporation of Delaware I \l\T,0/Drawing. Application November 30, 1940,

' Serial No. 368,048

6 Claims. (01. 260-673-5) This invention relates to the catalytic dehydrogenation of hydrocarbons. More particularly, the

invention relates to the conversion of aliphatic hydrocarbons having at least six carbon atoms per moleculeto aromatic hydrocarbons by denydrogenation and cyclization thereof.

The oxides of certain metals may be prepared in forms whereby they are active catalysts for the conversion of aliphatic hydrocarbons to aromatic hydrocarbons by dehydrogenation and cyclization thereof. A particularly active form of catalyst for this reaction is chromium oxide prepared by the formation of a chromium oxide gel which can be converted to a relatively dense granular material by such washing steps as may be required by reason of the method of preparation of the gel, and suitable drying.

In the conversion of aliphatic hydrocarbons to aromatic hydrocarbons by contact thereof with a gel-type chromium oxide catalyst the hydrocarbon vapors are passed over the catalyst at a temperature in the range of 325 to 650 0., preferably 400 to 500C. at atmospheric, or higher, pressure. The hydrocarbons are passed over the catalyst at a space velocity which may be varied in accordance with other operating conditions but should be sufiiciently low to produce a liquid product containing a substantial proportion of aromatic hydrocarbons. High rates of conversion of aliphatic hydrocarbons to aromatic hydrocarbons are associated with low space velocities and high reaction temperatures, and vice versa. At low temperatures withinthis range, therefore, a low space velocity may be employed while at higher temperatures a higher space velocity may be used, although these factors are conditions effective to produce 10 per cent or more of toluene in the liquid product the latter also contains 10 per cent or more of heptene. As the operating conditions are varied to increase the concentration of toluene in the liquid product to a figure greater than 10 per cent the percentage of heptene in the liquid product increases to a maximum of approximately 13 to 15 per v cent.

range of operating temperatures which are employed in connection with the use of the abovementioned metal oxide dehydrogenating cata- 1 lysts, whereby the modified catalysts are effective to 2 volumes of liquid per volume of catalyst per hour.

In the conversion of aliphatic paraflinic hydrocarbons to aromatic hydrocarbonsby contact with a gel-type chromium oxide under the preferred conditions defined above it is found that when these conditions are controlled to effect production of a substantial proportion of to promote the substantial conversion of aliphatic parafiinic hydrocarbons to aromatic hydrocarbons while producing normally liquid olefinio aliphatic hydrocarbons to a substantially lesser degree. For example, it has been discovered that the catalytic properties of gel-type chromium oxide can be thus modified by the incorporation therein of a substantial proportion of metallic nickel.

Nickel may be employed at certain temperatures as a catalyst for promoting the hydrogenation or dehydrogenation of hydrocarbons but at. the temperatures which are necessary in connection with the use of a metal oxide dehydrogenating catalyst nickel functions predominantly as a cracking catalyst.

The preparation of the modified catalyst of the present invention will be described by reference to an example of the preparation of a gel-type chromium oxide catalyst containing metallic nickel. It is to be understood, however, that such specific reference is for purposes of example and that the catalyst employed in the process of the invention may be prepared by any suitable method.

A modified gel-type chromium oxide catalyst suitable for use in connection with the present invention may be prepared advantageously'by aromatic hydrocarbons in the liquid product there occurs also a substantial production of unsaturated aliphatic hydrocarbons. For example,

in the conversion of heptane to toluene under effecting the co-precipitation of chromium oxide and nickel oxide under conditions wherein a gelatinous precipitate is formed. The gelatinous precipitate is then converted to a solid form by the methods of preparation customarily employed in the production of a gel-type chromium oxide catalyst. Thereafter the solid mixture of. chromium oxide and nickel oxide is subjected to suittion may be added slowly with stirring to a so1u-- tion which is 0.1 normal in chromium nitrate and 0.1 normal in nickel nitrate. Addition of the ammonium hydroxide to the salt solution is carriedout slowly with stirring in order to efiect formation of the desired gelatinous precipitate. After suitable washing and drying of the precipitate, with final heating of this material to 325 C., the dried material is subjected to treatment with hydrogen under conditions eifective to reduce the'nickel oxide to metallic nickel. The material thus prepared comprises a mixture of gel-type chromium. oxide 1 and finely divided metallic nickel in which the chromium and nickel are present in approximately equal molecular proportions.

Cracking catalysts such as nickel should be incorporated'in the catalytic material in aproportion sufllcient to efiect the desired modification of the catalytic properties of the metal oxide catalyst such as gel-type chromium oxide but not sufliciently great to change the essential character on the liquid product collected in approximately 88 minutes.

The results set forth in the table demonstrate that the chromium oxide-nickel catalyst is capable of converting heptane to liquid containing a substantial proportion of toluene and a proportion of heptane which is substantially less than of the metal oxide as a dehydrogenating catalyst.

The ratio of the constituents in the product of the foregoing example is satisfactory, but may be departed from by employing other suitable proportions. 4

. While the catalytic material employedin connection with the present invention suitably may consist of a mixture of the dehydrogenating and cracking catalysts suitable supporting material may be employed in addition to the essential constituents. For example, the mixture of chromium oxide and nickel oxide may be precipitated on a suitable supporting material'such as activated alumina, or the gelatinous mixture of these oxides may be suitably incorporated with supporting material after precipitation and prior to drying.

A chromium oxide-nickel catalyst prepared as described above and a corresponding gel-type chromium oxide catalyst free from nickel prepared by the same general method were tested for catalytic activity in the conversion of normal heptane to toluene. In these tests the heptane vapor was passed over the catalysts at atmospheric pressure and at a temperature of 425 C.

The liquid products obtained were analyzed for their content of olefinic hydrocarbons (heptene) and aromatic hydrocarbons (toluene). The results of the tests referred to are set forth in the following table.

Table Analysis of liquid products Space tal 8 Y: Weight Weight per cent per cent aromatics oleflns Chromium oxide l. 0 4. 4 11.7 Chromium oxide-nickel p 1.3 7.9 3.6

that obtained in connection with the use of chromium oxide catalysts containing no nickel. The testresults demonstrate that by employing the catalyst of the present invention heptane may be converted to a liquid product containing a proportion of aromatic hydrocarbons substantially greater than that produced by means of the chromium oxide catalyst, while effecting the formation in the liquid product of olefinic hydrocarbons in an amount less than half that produced by the chromium oxide catalyst. The test conditions favored the chromium oxide catalyst since it was tested at a lower space velocity than that of the test on the chromium oxide-nickel catalyst. As is pointed out above, in the use of a gel-type chromium oxide catalyst the rate of conversion of aliphatic hydrocarbons to aromatic hydrocarbons varies inversely to the space velocity. It would be expected, therefore, that theemployment of the chromium oxide catalyst at the same space velocity as that employed in connection with the chromium oxide-nickel catalyst would produce a liquid having an aromatic content substantially lower than that shown in the table'for the test employing the chromium I In the table the space velocities are given apoxide catalyst.

While the invention has been illustrated by reference to the treatment .of a single hydrocarbon compound the process is equally applicable to the treatment of mixtures of hydrocarbons. For example, the process may be applied to the dehydrogenation treatment of a gasoline of low anti-knock value to improve its anti-knock qualities. For example, a paraifinic naphtha may be treated to improve its anti-knock value by increasing the proportion of aromatic hydrocarbons therein while at the same time restricting the formation of olefinic hydrocarbons in the product. This permits the production of a gasoline which is relatively more stable and is particularly advantageous in ,meeting acid-heat specifications for aviation gasoline which require that the percentage of polymerizable materials contained in the gasoline shall be substantially restricted. The new process is advantageous also in the production of aromatic hydrocarbons where extraction of the aromatic hydrocarbons from the liquid product is complicated by the presence of substantial amounts of olefinic hydrocarbons.

We claim:

1. A process for the conversion of aliphatic hydrocarbons having at least six carbon atoms per molecule to aromatic hydrocarbons by dehydrogenation and cyclization thereof which comprises contacting said aliphatic hydrocarbons at a temperature of 325 to 650 C. with catalytic material comprising a mixture of a major proportion by weight of chromium oxide and a minor proportion of finely divided nickel.

2. A process for the conversion of aliphatic hydrocarbons having at least six carbon atoms per molecule-to aromatic hydrocarbons by dehydrogenation and cyclization thereof which comprises contacting said aliphatic hydrocarbons with a. catalyst comprising an intimate mixdivided nickel and maintaining said aliphatic hydrocarbons in contact with said catalyst at a hydrogenation and cyclization thereof which comprises contacting said aliphatic hydrocarbons with a catalyst comprising an intimate mixture of gel type chromium oxide and finely divided nickel and maintaining said aliphatic hydrocarbons in contact with said catalyst at a temperature sufficiently high and at a space velocity suificiently low to effect substantial conversion thereof to aromatic hydrocarbons by dehydrogenation and cyclization reactions.

4. A process for producing aromatics from aliphatic hydrocarbons of at least six carbon atoms in straight chain arrangement, which comprises contacting the aliphatic hydrocarbons with a catalyst comprising chromium sesquioxide and nickel and maintaining said aliphatic hydrocarbons in contact with said catalyst at a temperature sufiiciently high and at a space velocity sufliciently low to eflect substantial conversion thereof to aromatic hydrocarbons by dehydrogenation and cyclization reactions.

5. A process, fore the conversion of aliphatic hydrocarbons having at least six carbon atoms per molecule'to aromatic hydrocarbons by dehydrogenation and cyclization thereof which comprises contacting said aliphatic hydrocarbons with a catalyst essentially consisting of an intimate mixture of a major proportion of chromium oxide and a'minor proportion of finely divided nickel and maintaining said aliphatic hydrocarbons in contact with said catalyst at a temperature sufiiciently high and at a space velocity sufficiently low to efiect substantial con- 'version thereof to aromatic hydrocarbons by dehydrogenation and cyclization reactions.

6. A process for the conversion of aliphatic hydrocarbons having at least six carbon atoms per molecule to aromatic hydrocarbons by dehydrogenation and cyclization thereof which comprises contacting said aliphatic hydrocar-.

cyclization reactions.

HUGH S. TAYLOR. HAROLD FEHRER. 

